Investment Securities Available-for-Sale (Details 1) $ in Thousands	Mar. 31, 2018 USD ($) Number	Dec. 31, 2017 USD ($) Number
Available-for-sale securities in a continuous loss position, number of securities | Number	205	183
Available-for-sale securities in a continuous loss position, less than 12 months, estimated fair value	$ 296,120	$ 272,060
Available-for-sale securities in a continuous loss position, less than 12 months, unrealized losses	6,409	2,593
Available-for-sale securities in a continuous loss position, 12 months or greater, estimated fair value	200,808	203,046
Available-for-sale securities in a continuous loss position, 12 months or greater, unrealized losses	6,689	4,453
Available-for-sale securities in a continuous loss position, estimated fair value	496,928	475,106
Available-for-sale securities in a continuous loss position, unrealized losses	$ 13,098	$ 7,046
US Agency Securities [Member]
Available-for-sale securities in a continuous loss position, number of securities | Number	44	38
Available-for-sale securities in a continuous loss position, less than 12 months, estimated fair value	$ 113,476	$ 102,264
Available-for-sale securities in a continuous loss position, less than 12 months, unrealized losses	2,469	1,073
Available-for-sale securities in a continuous loss position, 12 months or greater, estimated fair value	54,634	55,093
Available-for-sale securities in a continuous loss position, 12 months or greater, unrealized losses	1,780	1,341
Available-for-sale securities in a continuous loss position, estimated fair value	168,110	157,357
Available-for-sale securities in a continuous loss position, unrealized losses	$ 4,249	$ 2,414
Residential Mortgage Backed Securities [Member]
Available-for-sale securities in a continuous loss position, number of securities | Number	148	137
Available-for-sale securities in a continuous loss position, less than 12 months, estimated fair value	$ 159,464	$ 152,350
Available-for-sale securities in a continuous loss position, less than 12 months, unrealized losses	3,326	1,306
Available-for-sale securities in a continuous loss position, 12 months or greater, estimated fair value	146,174	147,953
Available-for-sale securities in a continuous loss position, 12 months or greater, unrealized losses	4,909	3,112
Available-for-sale securities in a continuous loss position, estimated fair value	305,638	300,303
Available-for-sale securities in a continuous loss position, unrealized losses	$ 8,235	$ 4,418
Municipal Bonds [Member]
Available-for-sale securities in a continuous loss position, number of securities | Number	13	8
Available-for-sale securities in a continuous loss position, less than 12 months, estimated fair value	$ 23,180	$ 17,446
Available-for-sale securities in a continuous loss position, less than 12 months, unrealized losses	614	214
Available-for-sale securities in a continuous loss position, estimated fair value	23,180	17,446
Available-for-sale securities in a continuous loss position, unrealized losses	$ 614	$ 214